Spin freezing and the Sachdev-Ye model

TL;DR

This paper explores the connection between spin-freezing phenomena in Hund metals and the Sachdev-Ye model, providing insights into non-Fermi liquid behavior and unconventional superconductivity in correlated electron systems.

Contribution

It clarifies the relationship between spin-freezing in Hund metals and the Sachdev-Ye model, enhancing understanding of non-Fermi liquid properties and pairing mechanisms.

Findings

Spin-freezing leads to non-Fermi liquid behavior with $ ext{Im} ext{SelfEnergy} o oot ext{omega}$.

The Sachdev-Ye model captures key features of spin-freezing physics.

Spin fluctuations may induce electron pairing, relevant for unconventional superconductivity.

Abstract

Spin-freezing is the origin of bad-metal physics and non-Fermi liquid (non-FL) properties in a broad range of correlated compounds. In a multi-orbital lattice system with Hund coupling, doping of the half-filled Mott insulator results in a highly incoherent metal with frozen magnetic moments. These moments fluctuate and collapse in a crossover region that is characterized by unusual non-Fermi liquid properties such as a self-energy whose imaginary part varies $\propto \sqrt{\omega}$ over a wide energy range. At low enough temperature, the local moment fluctuations induce electron pairing and this mechanism may be the unifying principle of unconventional superconductivity. While this physics has been discovered in numerical studies of multi-orbital Hubbard systems, it exhibits a striking similarity to the analytically solvable Sachdev-Ye (SY) model, and its recent fermionic extensions. Here, we clarify the relation between spin-freezing and SY physics, and thus shed light on fundamental properties of Hund metals.